Jet propulsion power plants of the combustion turbine type



y 5, 1964 L. s. SNELL 3,131,536

JET PROPULSION POWER PLANTS OF THE COMBUSTION TURBINE TYPE Filed June 28, 1962 2 Sheets-Sheet 1 NVENTOR LEONARD S. SNELL imaawmm AT'IORN Eys.

y 5, 1964 L. s. SNELL 3,131,536

JET PROPULSION POWER PLANTS OF THE COMBUSTION TURBINE TYPE Filed June 28, 1962 v 2 Sheets-Sheet 2 NVENTOR LEONARD S. SNELL ATTORNEYS United States Patent 3,131,536 JET PROPULSEON FOWER PLANTS 6F THE COMBUSTIQN TURBiNE TYPE Leonard Stanley Snell, Harlow, England, assignor, by mesne assignments, to Bristol Siddeley Engines Limited, Bristol, England, a British company Filed .iune 28, 1962, Ser. No. 266,911

Claims priority, application Great Britain June 3%, 1961 4 Claims. (ill. 60-35.6)

, of the air compressor, and in which the products of combustion, after acting on the rotor of said main (or first) turbine, act on a second turbine the rotor of which is arranged to drive the rotor of a ducted fan before passing to and through one or more rearwardly directed hot gas propulsion nozzles, the ducted fan being arranged to deliver air through an air duct communicating with a further propulsion nozzle (hereinafter called for convenience a cold propulsion nozzle) so that the propulsive thrust produced by the power plant is due partly to the products of combustion passing from the turbines through the hot gas propulsion nozzle or nozzles and partly to the air delivered by the ducted fan to and through the cold propulsion nozzle.

For convenience herein the power plant will be assumed to be travelling in the direction in which it is urged by the thrust from the propulsion nozzle or nozzles and the terms forward and rear will be used in this sense.

Two main forms of jet propulsion power plant of the above kind have been proposed, namely that in which the fan is situated at the forward end of the power plant and is either connected to the rotor of the air compressor which is driven from the main turbine rotor of the power plant or is driven from a separate or second turbine rotor situated so as to receive the products of combustion after they have passed through the main (or first) turbine (this generally being referred to as a front fan), and that in which the fan is situated at the rear of the power plant and is driven from a separate second turbine rotor also situated at the rear of the power plant (in which case the fan is generally referred to as an aft fan).

With previous proposed forms of power plant having a front fan the air passing to the air compressor has had to pass through the front fan, while moreover, if the front fan rotor is driven from the compressor rotor this imposes limitations on the speed of the compressor rotor in order to avoid excessive tip speed of the front fan blades which are situated at a greater radial distance from the rotational axis than the blades of the compressor rotor. If on the other hand, with a front fan the fan rotor is driven from a separate (or second) turbine at the rear of the power plant this involves substantial constructional complications due to the necessity of employwhich reduces the acceleration.

In previous proposals for a power plant having an aft fan, while the aft fan can readily be driven by a second turbine rotor in rear of the first turbine rotor and the above difficulties associated with the use of a front fan tend, therefore, to be avoided, it is known that for a given total power output of a power plant the specific fuel consumption tends to be greater with the use of an aft fan than with a front fan since with the latter higher compression ratios can readily be obtained across the air compressor as a Whole and consequently higher mass flow through the high pressure stages of the air compressor.

It is an object of the present invention to provide a power plant of the kind referred to and of the front fan type which will minimize the previous disadvantages of front fan type plants and acquire to some extent certain advantages of previously proposed power plants of the aft fan type.

A jet propulsion power plant of the combustion turbine type according to the present invention comprises a high pressure air compressor of the axial flow type, having its air inlet situated adjacent the rear of the power plant, and arranged to deliver air forwardly within the power plant to one or more combustion chambers the products of combustion from which then pass forwardly through a first turbine the rotor of which is rigidly connected to the rotor of the high pressure air compressor and a second turbine the rotor of which is arranged in front of the first turbine rotor so as to be acted upon by the products of combustion after they have passed through the first turbine rotor, said second turbine rotor being connected to the rotor of a fan arranged to deliver air rearwardly from a forwardly facing air intake through air ducting displaced radially outwardly from the turbine rotors and the high pressure air compressor rotor, partly to a rearwardly facing cold propulsion nozzle and partly to the inlet of the high pressure air compressor, while the products of combustion after passing through the said second turbine are led through one or more radially outwardly extending conduits to and through one or more rearwardly directed hot gas propulsion nozzles.

In a simple arrangement, which might be adopted for power plants of relatively small size, the products of combustion may be led to the one or more hot gas propu sion nozzles through a single radially outwardly extending conduit lying within a circumferential are which subtends an angle at the axis of the turbine of substantially less than 360, for example of about 180, while at least that part of the air ducting through which the fan delivers air which extends axially past said conduit lies within a different circumferential arc.

In most cases, however, a series of circuinferentially spaced conduits will be provided for leading the products of combustion radially outwardly to the hot gas propulsion nozzle or nozzles, while the air ducting comprises an annular part in which the blades of the fan lie, a part in rear of said annular part which comprises a series of air ducts disposed between the hot gas conduits, and a further annular part in rear of such series of air ducts by which the air is led to the cold propulsion nozzle and the air inlet to the high pressure air compressor.

In any case the power plant may include an air passage, for example'in the form of a cuff, having a forwardly facing air inlet and a rearwardly facing outlet into which air passage the hot gas propulsion nozzle or nozzles eject the-products of combustion for the purpose of increasing the thrust obtained.

Vanes may be provided in the air ducting through which the fan delivers air to assist the guiding of air into the air inlet of the high pressure air compressor and/or in the conduit or conduits for the products of combustion to assist the required changes in the direction of flow of the products of combustion passing therethrough.

It will be seen that in power plants according to the invention the ducted fan constitutes in effect a low pressure compression stage for that part of the air which then passes to the high pressure compressor before being delivered to the combustion chamber or combustion chambers, the direction of air flow through such low pressure compression stage being opposite to that through the high pressure compressor.

Moreover with the invention the high pressure compressor and the first turbine may constitute a gas turbine engine of basic well-tried design to which the low pressure compression stage constituted by the ducted fan and the second turbine can be added. Further, such a basic design of engine may have added to it a variety of designs of low pressure fan and turbine units to provide a power plant according to the invention so that the appropriate design of the unit constituting the ducted fan and the second turbine driving it may be selected for application to the basic engine according to requirements.

It will also be apparent that where a power plant according to the invention is mounted in an aircraft, e.g. in an aircraft wing, the air will enter the power plant from the front, the air flow through the high pressure compressor will be from the rear towards the front, while the ejection of the products of combustion and of air through the hot and cold propulsion nozzles will be rearwardly.

The invention may be carried into practice in various ways but two embodiments of the invention will now be described by way of example with reference to the accompany drawings, in which:

FIGURE 1 is a cross section of a jet propulsion power plant according to the present invention in a plane containing the longitudinal axis of the power plant, and

FIGURE 2 is a similar view to that of FIGURE 1 of a modification of the power plant shown in FIGURE 1.

In the construction shown in FIGURE 1 the power plant comprises a basic combustion turbine engine 1 of known design having a casing 2, within which is supported the rotor of a multi-stage high pressure axial flow air compressor 3 mounted in bearings 4, the air inlet 5 of the compressor 3 is situated at the rear of the casing 2 and the compressor is arranged to deliver air forwardly to a number of combustion chambers 6 from which the products of combustion pass first forwardly to a main twostage turbine 7 the rotor 8 of which is rigid with the rotor 9 of the compressor 3. Rigidly secured to the forward end of the casing 2 is a ducted fan assembly 11 comprising a casing 12 in which is supported on bearings 13 a shaft 14 carrying a turbine rotor 15 and a fan rotor 16, the turbine rotor 15 being arranged to be acted upon by the products of combustion after they have passed forwardly through the turbine 7 The blades of the fan 15 are arranged to receive air from a forwardly facing air intake 17 at the front of the power plant provided with inlet guide vanes 18, and the fan delivers such air rearwardly through ducting 19 comprising an annular part 20 across which the fan blades extend, a part 21 in rear of the fan across which a series of conduits 22 for the products of combustion extend, and a further annular part 23 by which air is led partly to a cold propulsion nozzle 24 and partly to the air inlet 5 of the compressor 3.

The conduits 22 lead the products of combustion from the turbine rotor 15 across the air ducting 19 to an annular rearwardly directed hot gas propulsion nozzle 25 which lies radially outside the air ducting I? and it will be understood that the parts of the conduits 22 which extend across the air ducting 19 will be of appropriate streamlined shape or be enclosed in fairings of that shape in order to facilitate the passage of air past them. It will be seen that the conduits 22 reverse the direction of flow of the products of combustion after leaving the turbine 7 and to assist in guiding the products of combustion guide vanes 26 are provided in the conduits 22. Further it will be seen that the part of the air flowing through the air ducting 19 which is delivered to the compressor 3 also has its direction of flow reversed and to assist in the change of direction of this portion of the air stream guide vanes 27 are provided adjacent to the air inlet 5.

The power plant shown in FIGURE 2. is identical to that shown in FIGURE 1 except that a cuff 28 is provided which extends along the power plant and which forms an annular air passage 29 outside the casings 2 and 12. The same reference numerals have been given to the other parts of the power plant as in FIGURE 1 and these parts will not be again described. In this construction the products of combustion are led into the passage 29 by the conduits 22 and hot gas propulsion nozzle 25 and are mixed with air entering the forward end of the passage 29 and are ejected from a nozzle 30 constituted by the after end of the cuff 28, which thus constitutes in effect a combined hot gas and air nozzle.

It will be appreciated that, where in the illustrated embodiments a simple hot gas propulsion nozzle of annular form is shown, two or more separate nozzles may instead be distributed around the air ducting.

It will be apparent that in the constructions shown, although the part of the air ducting across which the conduits extend is annular, the question of whether this part of the air ducting is constructed from annular parts and the conduits are tubular, or the conduits are formed by annular parts across which tubular air ducts extend is a matter of constructional detail only and that in each case the structure provides a series of axially extending air ducts between which lie radially extending conduits.

What I claim as my invention and desire to secure by Letters Patent is:

1. A jet propulsion power plant of the combustion turbine type comprising an axial flow high pressure air compressor having a rearwardly facing air inlet, at least one combustion chamber situated in front of said air compressor and arranged to receive air therefrom, a first turbine rotor situated in front of said combustion chamber to be acted upon by the products of combustion therefrom and connected to said rotor of said air compressor, a ducted fan assembly comprising a second turbine rotor situated in front of said first turbine rotor and arranged to be acted upon by said products of combustion after passing through said first turbine rotor and a fan rotor situated in front of and axially spaced from said second turbine rotor, said fan rotor being directly connected to said second turbine rotor and carrying at least one row of fan blades, air ducting displaced radially outwardly from the turbine rotors and in which said fan blades lie to act on the air therein to impel the air in a rearward direction, an air propulsion nozzle through which part of said air is ejected, said air inlet of said air compressor receiving the remainder of said air, hot gas ducting extending across said air ducting at a point in front of said second turbine rotor and in rear of said fan rotor and arranged to receive said products of combustion after they have passed through said second turbine rotor, and at least one rearwardly directed hot gas propulsion nozzle situated outside said air ducting and connected to said hot gas ducting.

2. A power plant as claimed in claim 1, in which said air ducting comprises an annular part in which said blades of said fan rotor lie, at part in rear of said annular part comprising a series of axially extending air ducts, and a further annular part in rear of said air ducts, and in which said hot gas ducting comprises a series of radially outwardly extending hot gas ducts interposed between said axially extending air ducts, said rearwardly directed hot gas propulsion nozzles being connected respectively to said hot gas ducts.

3. A power plant as claimed in claim 2 including annular vanes the outer edges of which lie immediately in rear of said further annular part of said air ducting while their inner edges lie immediately in rear of said air inlet whereby said vanes serve to deflect part of the air flowing through said further annular part into said air inlet while permitting the remainder of said air to flow rearwardly through said air nozzle.

4. A power plant as claimed in claim 1 in which a cuff is provided outwardly spaced from said rearwardly directed hot gas propulsion nozzle so that said products of combustion are ejected into an annular air passage formed by said cutf.

References Cited in the file of this patent UNITED STATES PATENTS 2,504,181 Constant Apr. 18, 1950 2,505,660 Baumann Apr. 25, 1950 3,069,848 Gl'iffith Dec. 25, 1962 

1. A JET PROPULSION POWER PLANT OF THE COMBUSTION TURBINE TYPE COMPRISING AN AXIAL FLOW HIGH PRESSURE AIR COMPRESSOR HAVING A REARWARDLY FACING AIR INLET, AT LEAST ONE COMBUSTION CHAMBER SITUATED IN FRONT OF SAID AIR COMPRESSOR AND ARRANGED TO RECEIVE AIR THEREFROM, A FIRST TURBINE ROTOR SITUATED IN FRONT OF SAID COMBUSTION CHAMBER TO BE ACTED UPON BY THE PRODUCTS OF COMBUSTION THEREFROM AND CONNECTED TO SAID ROTOR OF SAID AIR COMPRESSOR, A DUCTED FAN ASSEMBLY COMPRISING A SECOND TURBINE ROTOR SITUATED IN FRONT OF SAID FIRST TURBINE ROTOR AND ARRANGED TO BE ACTED UPON BY SAID PRODUCTS OF COMBUSTION AFTER PASSING THROUGH SAID FIRST TURBINE ROTOR AND A FAN ROTOR SITUATED IN FRONT OF AND AXIALLY SPACED FROM SAID SECOND TURBINE ROTOR, SAID FAN ROTOR BEING DIRECTLY CONNECTED TO SAID SECOND TURBINE ROTOR AND CARRYING AT LEAST ONE ROW OF FAN BLADES, AIR DUCTING DISPLACED RADIALLY OUTWARDLY FROM THE TURBINE ROTORS AND IN WHICH SAID FAN BLADES LIE TO ACT ON THE AIR THEREIN TO IMPEL THE AIR IN A REARWARD DIRECTION, AN AIR PROPULSION NOZZLE THROUGH WHICH PART OF SAID AIR IS EJECTED, SAID AIR INLET OF SAID AIR COMPRESSOR RECEIVING THE REMAINDER OF SAID AIR, HOT GAS DUCTING EXTENDING ACROSS SAID AIR DUCTING AT A POINT IN FRONT OF SAID SECOND TURBINE ROTOR AND IN REAR OF SAID FAN ROTOR AND ARRANGED TO RECEIVE SAID PRODUCTS OF COMBUSTION AFTER THEY HAVE PASSED THROUGH SAID SECOND TURBINE ROTOR, AND AT LEAST ONE REARWARDLY DIRECTED HOT GAS PROPULSION NOZZLE SITUATED OUTSIDE SAID AIR DUCTING AND CONNECTED TO SAID HOT GAS DUCTING. 